1. Field of the Invention
The present invention relates to an improvement of a magnetic sensor for reading the information recorded in magnetic recording media. More particularly, the invention relates to an improvement of a magnetoresistance element and head, a magnetoresistance sensing system, and a magnetic storing system.
2. Description of the Related Art
In the magnetic recording fields, conventionally, magnetoresistive (MR) read transducers termed the xe2x80x9cmagnetoresistance (MR) sensorsxe2x80x9d or xe2x80x9cmagnetoresistance (MR) headsxe2x80x9d have already been developed and actually used. It has been well known that the MR sensors are capable of reading information from the surface of magnetic recording media at high linear densities.
The MR sensors sense magnetic signals by way of the electrical resistance change of MR elements that varies as a function of the strength and orientation of the magnetic flux sensed by read or MR elements. The MR sensors operate on the basis of the well-known anisotropic magnetoresistance (AMR) effect that a component of the electrical resistance of the MR element varies proportional to the square or the cosine one of the angle between the magnetization orientation of the element and the sense current flowing through the element.
The AMR effect was explained in detail in the paper written by D. A. Thompson et al. and entitled xe2x80x9cMemory, Storage, and Related Applicationsxe2x80x9d, IEEE Transaction on Magnetics, Vol. MAG-11, No. 4, pp. 1039-1050, July 1975.
With the conventional magnetic sensors using the AMR effect, vertical magnetic bias has been typically applied to suppress the Barkhausen noise. To realize the vertical magnetic bias, proper antiferromagnetic substance, such as FeMn, NiMn, or oxide of Ni, has been often used as the vertically biasing material.
In recent years, more distinctive MR effect termed the xe2x80x9cgiant MR effect (GMR)xe2x80x9d or xe2x80x9cspin valve effectxe2x80x9d observed in multi-layered MR sensors of specific sorts has been reported. It has been said that the GMR or spin valve effect is caused by the following reason.
Specifically, if the multl-layered MR sensor has a structure comprising a pair of ferromagnetic layers and a nonmagnetic layer disposed between the pair of ferromagnetic layers, the large electrical resistance change of the MR sensor is due to the spin-dependent transmission of conduction electrons between the pair of ferromagnetic layers by way of the nonmagnetic layer and the spin-dependent scattering at their interfaces accompanied by the spin-dependent transmission.
MR sensors using the GMR effect have improved sensitivity compared with those using the AMR effect, increasing the electrical resistance change of the sensors. When the MR sensor has the above-identified structure comprising a pair of ferromagnetic layers and a nonmagnetic layer disposed between the pair of ferromagnetic layers, it has been found that the in-plane electrical resistance of the sensor is proportional to the cosine of the angle between the magnetization orientations of the pair of ferromagnetic layers.
Concrete configurations of the conventional MR sensors or heads using the GMR or spin valve effect have been disclosed in the following publications.
The Japanese Non-Examined Patent Publication No. 2-61572 published in March 1990 disclosed a MR sensor having a multi-layered structure of at least two ferromagnetic layers and an intermediate layer, which generates large electrical resistance change due to antiparallel arrangement of magnetization in the ferromagnetic layers. As the magnetic layers, several ferromagnetic transition metals and alloys are disclosed. An antiferromagnetic layer, which is preferably made of FeMn, may be formed to contact with one of the ferromagnetic layers.
The Japanese Non-Examined Patent Publication No. 4-358310 published in December 1992 disclosed a MR sensor having a multi-layered structure of a pair of ferromagnetic layers and an intervening nonmagnetic layer. In this sensor, when the applied external magnetic field has a value of zero, the magnetization orientations of the pair of ferromagnetic layers are perpendicular to each other. The electrical resistance of the MR sensor varies proportional to the cosine of the angle between the magnetization orientations of the pair of ferromagnetic layers and is independent upon the orientation of the current flowing through the sensor.
The Japanese Non-Examined Patent Publication No. 6-203340 published in July 1994 disclosed a MR sensor having a multi-layered structure of a pair of ferromagnetic layers and an intervening nonmagnetic layer. In this sensor, the magnetization easy axes of the pair of ferromagnetic layers are substantially parallel to each other. When an external magnetic field is applied, the induced magnetization orientations of the pair of ferromagnetic layers are shifted in opposite directions to each other with respect to their magnetization easy axes.
The Japanese Non-Examined Patent Publication No. 9-282618 published in October 1997 disclosed a MR head having a MR or spin valve layer with a multi-layered structure, a pair of domain control layers disposed at each side of the MR layer, and a pair of electrodes disposed on the pair of domain control layers and electrically connected to the MR layer. In this head, the MR layer has a size corresponding to the track width of a magnetic recording medium. The pair of electrodes are partially overlapped with the MR layer. The distance between the pair of electrodes is narrower than the width of the MR layer.
FIG. 1 shows an example of the configuration of the prior-art MR heads, which is a cross-sectional view taken along the Air Bearing Surface (ABS).
As shown in FIG. 1, the prior-art MR head 110 comprises a lower shielding layer 101 formed on the surface of a substrate 111. A lower gap layer 102 is formed on the lower shielding layer 101. A MR layer 103 and a pair of vertical biasing layers 104 are selectively formed on the lower gap layer 102.
The MR layer 103 has an approximately trapezoidal cross section, as shown in FIG. 1. The width of the MR layer 103 is approximately equal to the track width of applicable magnetic recording media (not shown).
The pair of vertical biasing layers 104 are disposed at each side of the MR layer 103. The inner opposing ends of the biasing layers 104 are respectively overlapped with and contacted with the corresponding inclined ends of the MR layer 103.
A pair of electrode layers 106 are formed on the pair of biasing layers 104 and the MR layer 103. The inner opposing ends of the electrode layers 106 are apart from each other by the intervening gap and are contacted with the upper surface of the MR layer 103, thereby electrically connecting the electrode layers 106 to the layer MR 103. The middle region of the MR layer 103 in its widthwise direction is exposed through the gap intervening between the electrode layers 106.
The MR layer 103, the pair of biasing layers 104 and the pair of electrode layers 106 constitute a MR element 109.
An upper gap layer 107 is formed on the pair of biasing layers 104 and the exposed MR layer 103. The exposed middle region of the MR layer 103 is covered with the upper gap layer 107. An upper shielding layer 108 is formed on the upper gap layer 107.
The lower shielding layer 101, the lower gap layer 102, the MR element 109, the upper gap layer 107, and the upper shielding layer 108 constitute the prior-art MR head 110.
With the prior-art MR head 110, the inner opposing ends of the electrode layers 106 are disposed to be nearer to the middle of the MR layer 103 than the contacting parts of the vertical biasing layers 104 with the MR layer 103. In other words, when the centerline of the MR layer 103, which corresponds to the centerline of applicable magnetic recording media in the tracking direction, is defined as C, as shown in FIG. 1, the innermost edges of the electrode layers 106 are located to be nearer than the innermost edges of the biasing layers 104 in the MR element 109.
Accordingly, with the MR element 109 having the above-described configuration, the magnetization of the MR layer 103 is fixed in its innermost edges by the biasing layers 104, thereby eliminating the sensitivity of the element 109 to the leakage magnetic field from the magnetic recording media. In other words, since the MR layer 103 that serves as the magnetic sensing region is domain-controlled, the Barkhausen noise is suppressed. Also, the sense current supplied by the electrode layers 106 flows through only the vicinity of the middle region of the MR layer 103 without flowing through its end regions (i.e., with bypassing its end regions). As a result, high magnetic sensitivity is realized and thus, the output of the reproduction head (i.e., the reproduction output) is enlarged. In this way, high magnetic sensitivity and good domain control in the sensing region can be realized, thereby raising the reproduction output with suppressing the Barkhausen noise.
However, when the inventor, K. Hayashi, actually produced the above-described prior-art MR head 110 and examined its operation and performance, he found that the sense current tended to flow through nor only the middle region of the MR layer 103 but also its outer regions. As a result, the effective track width of the MR head 110 that serves as the reproduction head is wider than the distance between the inner opposing edges of the electrode layers 106 (i.e., the interval between the electrode layers 106). This raises a problem that narrowing of the effective track width is difficult to realized.
Accordingly, an object of the present invention is to provide a MR element and a MR head that allow the sense current to flow through only the middle part of the inner region of a MR layer and its vicinity to bypass its end regions, thereby realizing high magnetic sensitivity and good domain control in the sensing region.
Another object of the present invention is to provide a MR element, a MR head, a MR sensing system, and a magnetic recording system that suppress the increase of the effective track width, thereby narrowing the read track easily.
Still another object of the present invention is to provide a MR element, a MR head, a MR sensing system, and a magnetic recording system that suppress effectively the Barkhausen noise even if the effective reproduction track width is narrowed.
The above objects together with others not specifically mentioned will become clear to those skilled in the art from the following description.
According to a first aspect of the present invention, a MR element is provided, which comprises;
(a) a MR layer having a width corresponding to a recording track width of an applicable magnetic recording medium;
(b) a pair of vertical biasing layers disposed at each side of the MR layer to be overlapped with each end of the MR layer;
inner opposing ends of the pair of vertical biasing layers being contacted with the MR layer;
(c) a pair of dielectric layers formed on the pair of biasing layers;
inner opposing ends of the pair of dielectric layers being contacted with the MR layer; and
(d) a pair of electrode layers formed on the pair of dielectric layers;
inner opposing ends of the pair of electrode layers being contacted with the MR layer, thereby electrically connecting the pair of electrode layers to the MR layer;
a distance between the inner opposing ends of the pair of electrode layers being smaller than a width of the MR layer.
With the MR element according to the first aspect of the present invention, the pair of vertical biasing layers are disposed at each side of the MR layer to be overlapped with each end of the MR layer and the inner opposing ends of the pair of vertical biasing layers are contacted with the MR layer. The pair of dielectric layers are formed on the pair of biasing layers and the inner opposing ends of the pair of dielectric layers are contacted with the MR layer. The pair of electrode layers are formed on the pair of dielectric layers and the inner opposing ends of the pair of electrode layers are contacted with the MR layer, thereby electrically connecting the pair of electrode layers to the MR layer. The distance between the inner opposing ends of the pair of electrode layers is smaller than a width of the MR layer.
Accordingly, the sense current, which flows through the pair of electrode layers and the MR layer, does not enter the one of the two end regions of the MR layer and does not exit out of the other directly or by way of the pair of vertical biasing layers.
On the other hand, the inner opposing ends of the pair of vertical biasing layers are contacted with the end regions of the MR layer and therefore, the orientation of magnetization is fixed and the sensitivity to an external magnetic flux is zero in the end regions of the MR layer. Unlike this, the sensitivity to an external magnetic flux of the MR layer increases gradually toward its center and thus, it is high in the middle part of the inner region of the MR layer while it is intermediate in its intermediate regions between the middle part and each end region.
Moreover, because the inner opposing ends of the pair of dielectric layers are contacted with the MR layer, the possibility that the sense current enters the intermediate regions of the MR layer having an intermediate sensitivity to an external magnetic flux is approximately cancelled.
As a result, the sense current is controlled or guided to flow through the middle part or the inner region of the MR layer having a high sensitivity to an external magnetic flux. This means that the output of the MR layer is increased and at the same time, the effective reproducing track width is narrowed (i.e., the track density is increased).
In addition, since the inner opposing ends of the pair of vertical biasing layers are contacted with the MR layer, the dynamic coercive force of the MR layer is suppressed sufficiently. Thus, good domain control is accomplished and the Barkhausen noise is effectively suppressed.
According to a second aspect of the present invention, another MR element is provided, which comprises:
(a) a MR layer;
(b) a pair of vertical biasing layers disposed at each side of the MR layer to be overlapped with each end of the MR layer;
inner opposing ends of the pair of vertical biasing layers being contacted with the MR layer;
(c) a pair of electrode layers formed on the pair of biasing layers;
innermost ends of the pair of electrode layers being located more inwardly than innermost ends of the pair of vertical biasing layers;
the pair of electrode layers being electrically connected to the MR layer;
(d) a pair of dielectric layers formed to overlap with the pair of biasing layers and the MR layer;
each of innermost ends of the pair of dielectric layers being located between one of the innermost ends of the pair of electrode layers and a corresponding one of the innermost ends of the pair of vertical biasing layers.
With the MR element according to the second aspect of the present invention, because of substantially the same reason as that of the MR element according to the first aspect, the same advantages as those in the MR element of the first aspect are given.
According to a third aspect of the present invention, a MR head is provided, which comprises:
(a) a lower shielding layer formed on a substrate;
(b) a lower dielectric gap layer formed on the lower shielding layer;
(c) the MR element according to the first or second aspect of the invention;
(d) an upper dielectric gap layer formed on the MR element; and
(e) an upper shielding layer formed on the upper dielectric gap layer.
With the MR head according to the third aspect of the present invention, because of substantially the same reason as that of the MR element according to the first aspect, the same advantages as those in the MR element of the first aspect are given.
According to a fourth aspect of the present invention, a MR sensing system is provided, which comprises:
(a) the MR element according to the first or second aspect of the invention;
(b) means for generating a current flowing through the element;
(c) means for sensing an electrical resistance change of the element as a function of a magnetic field to be sensed by the element.
With the MR sensing system according to the fourth aspect of the present invention, because of substantially the same reason as that of the MR element according to the first aspect, the same advantages as those in the MR element of the first aspect are given.
According to a fifth aspect of the present invention, another MR sensing system is provided, which comprises:
(a) the MR head according to the third aspect of the invention;
(b) means for generating a current flowing through the element;
(c) means for sensing an electrical resistance change of the element as a function of a magnetic field to be sensed by the element.
With the MR sensing system according to the fifth aspect of the present invention, because of substantially the same reason as that of the MR element according to the first aspect, the same advantages as those in the MR element of the first aspect are given.
According to a sixth aspect of the present invention, a magnetic storing system is provided, which comprises:
(a) a magnetic recording subsystem for recording information in a magnetic recording medium having information-recording tracks;
(b) the MR sensing system according to the fourth or sixth aspect of the invention; and
(c) actuator means for moving the magnetic recording subsystem and the MR sensing system to a selected one of the tracks of the medium;
the actuator means being associated with the magnetic recording subsystem and the MR sensing system.
With the magnetic storing system according to the sixth aspect of the present invention, because of substantially the same reason as that of the MR element according to the first aspect, the same advantages as those in the MR element of the first aspect are given.